Dick, To hopefully answer your questions:
1 - The Digitrax BD-4 is a current detector and it looks like the type that looks for a voltage drop across a diode or diodes. It should detect any locomotive with a decoder in it. The decoders draw some current even when all functions are off because the processor is still working looking for its control signal. The BD-4 will only detect rolling stock that has some current draw (decoder, light, resistor wheelsets), but it sounds like you only need to detect the locomotive. If you read the manual (pdf on Digitrax's website) it tells you how to desensitize the detector by adding a resistor; which to me indicates that if anything it is on the oversensitive side. 2 - I don't have one to try, but I don't think you'll have a problem. If you use more than one LED, they just might not be quite as bright. It is dependent on the actual LED's you use and the value of the current limiting resistor on the BD-4. You could ask at Litchfield Station; they are knowledgeable about Digitrax. You should be able to add a transistor to the output if you need to switch more current, but I doubt if need to get that complicated. The common detection methods are: 1 - Infrared Optical Detector - These are really a point detector although if you angle the beam, you can cover a siding. 2 - Current Drop Across Diode - Probably the most common detector and low cost. The main disadvantage is there is a voltage drop across the diode(s), so trains can slow down going from a nodetected to a detected track section. This shouldn't be a problem in a staging yard. The BD-4 falls into this class. Bruce Chubb's optimized detector is a well known DIY version of this type of detector. 3 - Current Transformer Type - Because the DCC track voltage is basically an AC square wave, a current transformer can be used to detect load current on a track section. These are more expensive than the diode drop type, but there is no voltage drop difference between detected and undetected track sections. The transformer also inherently isolates the track from the signal circuit without the need for using optoisolators. NCE's BD-20 and Bruce Chubb's DCCOD are two of this type. Now, if you want to know the engine or train ID, then you are into more complicated systems, such as Railcom (NMRA bi-directional), Digitrax's transponding, or Zimo's system and you are limited on decoder support. Dave Heine -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Richard Karnes Sent: Wednesday, July 23, 2008 1:56 AM To: S-Scale Subject: {S-Scale List} More DCC requirements All you DCC people -- Having converted my layout to DCC, I lately came to realize that I could do away with the dispatcher position -- a nearly hidden cubicle (beneath a mountain) with two panels that control both the power and the turnouts for each of two four-track staging yards. All of the eight staging-yard tracks are now "live," so having the dispatcher activate or kill the staging tracks was no longer necessary. Without this requirement, I got to thinking about the turnout controls for the staging-yard ladders (four of them). With no need to control power to the staging tracks anymore, I got mighty tired of crawling into the dispatcher's cubbyhole just to throw a couple of turnouts. The final light-bulb moment: I could remove the block toggles, split the turnout control panels, and relocate each adjacent to the ladder it controls. I have concluded this exercise for both four-track staging yards - New York/Springfield beneath a mountain and New Haven/Pittsfield beneath the Port Hudson harbor. There are now four small separate staging ladder turnout panels at four different layout locations, each adjacent to the ladder it controls. Henceforth, the erstwhile dispatcher will simply have to run trains. So now I have one more requirement: I need to install track-occupancy detectors on each of the four tracks in the invisible staging yard - the one under the mountain. I have found a device that might do the job, the Digitrax 245-BD4, described at http://www.prototypicalmodeltrains.com/site/1324105/product/245-BD4. From the description I think this will do the job for all four tracks. But I am not well versed in electronics, so I am appealing to those of you who are. I have a couple questions: 1. Will this device detect the presence of a locomotive equipped with a decoder even when it is not being addressed by the DCC command station? Or do I have to install lights in every loco in order to draw some track power, and thus be recognized? 2. Can I attach two LEDs to each of the four detectors rather than one, so I can have an occupancy indicator on each of the two widely separated yard-ladder turnout control panels? I can get this $30 item from Litchfield Station for $24. But should I be using "old" technology such as infrared (optical) detectors? Would these be simpler and not a lot more expensive? Dick Karnes [Non-text portions of this message have been removed] ------------------------------------ Yahoo! Groups Links ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/S-Scale/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/S-Scale/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
